The present invention relates to a method and an apparatus for detecting decrease in tire air-pressure as well as a selecting program for thresholds for judging decompression of a tire. More particularly, it relates to a method and an apparatus for detecting decrease in tire air-pressure as well as a selecting program for thresholds for judging decompression of a tire which is capable of improving the accuracy of a detection of decompression.
A conventional apparatus for detecting decrease in tire air-pressure (DWS system) judges a decompressed condition of a tire based on information of four ABS wheel speed sensors. For judging decompression of a tire in this apparatus, a judged value is employed in which a difference between two diagonal sums of front wheel tires and rear wheel tires is compared. Since a single threshold is used for judging anomalies in air-pressure of the four wheel tires, an alarm for indicating an abnormality of the tire air-pressure is generated no matter which of the tires of the driving wheels and the follower wheels are abnormal.
However, it can be understood, from data as illustrated in FIG. 4 in which a FF (front engine/front drive) vehicle (Accord produced by Honda Motor Co., Ltd. with tire sizes of 205/60R15) mounted with either a front left tire (driving wheel) FL or a rear left tire (follower wheel) RL of which air-pressure has been decompressed by 30% was made to perform running, that values for judging abnormalities in air-pressure (judged value) are different between the driving wheel FL and the following wheel RL although the decompressed conditions are identical at 30%.
When employing the current technique in which a threshold is used which is set to be lower than the judged value for the following wheel RL but higher than the judged value for the driving wheel FL, it is impossible to judge an abnormal condition of the air-pressure unless the degree of decompression of the driving wheel tire FL is high whereas an abnormal condition of the following wheel RL is detected already at a low degree of decompression.
The present invention has been made in view of the above facts, and it is an object thereof to provide a method and an apparatus for detecting decrease in tire air-pressure as well as a selecting program for thresholds for judging decompression of a tire which are capable of improving the accuracy of detection of decompression.
In accordance with a first aspect of the present invention, there is provided a method for detecting decrease in tire air-pressure for detecting decrease in internal pressure of a tire on the basis of rotational information obtained from tires attached to a vehicle, wherein a threshold for judging decrease in air-pressure of following wheels is different from a threshold for judging decrease in air-pressure of driving wheels.
In accordance with a second aspect of the present invention, there is provided an apparatus for detecting decrease in tire air-pressure for detecting decrease in internal pressure of a tire on the basis of rotational information obtained from tires attached to a vehicle, comprising: a rotational information detecting means for detecting rotational information of respective tires; a steering angle detecting means for detecting a steering angle; a memory means for storing the rotational information of the respective tires and the steering angle; a straight-ahead drive judging means for judging, based on the steering angle, whether the vehicle is performing straight-ahead driving; a turning radius calculating and processing means for calculating a turning radius on the basis of the rotational information of the tires; a comparing and determining means for determining, on the basis of the turning radius as calculated by the turning radius calculating and processing means, whether the vehicle is performing straight-ahead driving or not in case it has been determined on the basis of the steering angle that the vehicle is performing straight-ahead driving; a threshold selecting means for selecting a threshold for judging decrease in air-pressure on the basis of the determination of the comparing and determining means; and a judged value calculating and processing means for calculating a judged value of decompression of air-pressure on the basis of the threshold.
In accordance with a third aspect of the present invention, there is provided a selecting program for a threshold for judging decompression of a tire which is so arranged that, for selecting a threshold for judging decrease in tire air-pressure, a computer is made to function as a rotational information detecting means for detecting rotational information of respective tires, a steering angle detecting means for detecting a steering angle, a memory means for storing the rotational information of the respective tires and the steering angle, a straight-ahead drive judging means for judging, based on the steering angle, whether the vehicle is performing straight-ahead driving, a turning radius calculating and processing means for calculating a turning radius on the basis of the rotational information of the tires, a comparing and determining means for determining, on the basis of the turning radius as calculated by the turning radius calculating and processing means, whether the vehicle is performing straight-ahead driving or not in case it has been determined on the basis of the steering angle that the vehicle is performing straight-ahead driving, and a threshold selecting means for selecting a threshold for judging decrease in air-pressure on the basis of the determination of the comparing and determining means, and a judged value calculating and processing means for calculating a judged value of decompression of air-pressure on the basis of the threshold.